Capacitive discharge ignition system employing a saturable switching core and a transistor



p 1968 0 0. K. NILSSEN CAPACITIVE DISCHARGE IGNITION SYSTEM EMPLOYING A SATURABLE SWITCHING CORE AND A TRANSISTOR Filed June 25, 1965 T NSF OLE K. N/L $55M INVENT? B I I ATTORNEYS United States Patent O CAPACITIVE DISCHARGE IGNITION SYSTEM EM- PLOYING A SATURABLE SWITCHING CORE AND A TRANSISTOR Ole K. Nilssen, Livonia, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed June 25, 1965, Ser. No. 466,948 4 Claims. (Cl. 315-205) ABSTRACT OF THE DISCLOSURE An ignition system for an internal combustion engine in which a capacitor is charged to a substantially constant electrical energy level just prior to the time for the requirement of ignition voltages. The charging of the capacitor may be done through a metering device comprising a saturable switching core and a solid state switching device upon the requirement for ignition voltages. The saturable switching core and the solid state switching device act to discharge the capacitor through the primary winding of the ignition coil. The capacitor in this case is charged to a sufficient voltage to permit voltages of a sufficiently high level to be induced in the secondary winding of the ignition coil to break down the spark gap of the ignition device or the spark plug. The charging mechanism or device for the capacitor may include an inductor connected in series with the output electrodes of the solid state switching device and one terminal of the source of electrical energy which may comprise an electrical storage battery. In addition, a unilateral conducting device may be positioned in series with the inductor and the one terminal of the source of electrical energy and is poled to permit current flow from the inductor to the one terminal of the source of electrical energy or electrical storage battery and to prevent current fiow from this terminal through the inductor. Hence, the electrical energy that is stored in the inductor may flow into the capacitor to charge it to its proper operating level.

This invention relates to an ignition system for an internal combustion engine, and more particularly to an ignition system for an internal combustion engine in which a capacitor is charged to a substantially constant electrical energy level just prior to the time for the requirement of ignition voltages and in which the high voltage necessary for the breakdown of the ignition device or spark plug is supplied by the electrical energy discharge from the capacitor. The system may also include means for supplying a lower voltage required for are sustaining through the ignition device or spark plug directly from the source of electrical energy of the system after the discharge of the capacitor.

In the invention, a capacitor coupled to a primary winding of an ignition coil is charged to a substantially constant energy level immediately prior to the requirement for ignition voltages. This may be done through a metering device comprising a saturable switching core and a solid state switching device. Upon the requirement for ignition voltages, the saturable switching core and the solid state switching device act to discharge the capacitor through the primary winding of the ignition coil. The capacitor is charged to a sufiicient voltage to permit voltages of a sufiiciently high level to be induced in the secondary winding of the ignition coil to break down the spark gap of the ignition device or spark plug. Immediately after this discharge, the primary winding of the ignition coil may be connected to the battery so that the lower voltage required for are sustaining is obtained directly from the battery.

This system utilizes the metering device comprised of the saturable switching core or transformer and the solid 3,400,300 Patented Sept. 3, 1968 state switching device disclosed in my copending application S.N. 403,263, filed Oct. 12, 1964, Pat. No. 3,312,210. The present invention provides all of the advantages of the invention disclosed in that application, but in addition provides a system in which the currently used ignition timing mechanism for an internal combustion engine need not be altered or changed in any way. In the invention, the capacitor is discharged immediately upon the opening of the ignition contact breaker points, and hence it is analogous to interrupting current in the primary winding of the ignition coil by the opening of a set of ignition contact breaker points.

An object of the present invention is the provision of an efiicient ignition system for an internal combustion engine that provides sufiicient ignition voltages during all engine operating conditions and that provides low current drain on the source of electrical energy during all of these conditions.

Another object of the invention is the provision of an ignition system in which initial high ignition voltages are obtained from the discharge of a capacitor and lower voltages required for are sustaining in the ignition device are obtained directly from the source of electrical energy of the system.

A further object of the invention is the provision of a capacitive type discharge system for an internal combustion engine in which a constant amount of electrical energy is supplied to the capacitor prior to the requirement for ignition voltages independently of and irrespective of the speed of the internal combustion engine utilizing the system.

Referring now to the drawings in which like reference numerals designate like parts throughout the several views thereof, there is shown in FIGURE 1 a circuit diagram of the present invention;

FIGURE 2 discloses a hysteresis loop of the saturable switching core or transformer utilized with the system, and

FIGURE 3 indicates the voltage output waveform that may be developed in the ignition system.

Referring now to FIGURE 1, there is shown a schematic electrical diagram of the ignition system of the present invention in which an ignition coil 10 has a primary winding 11 and a secondary winding 12. The secondary winding 12 is connected through lead 13 to a rotating arm 14 of a distributor 16. The rotating arm 14 sequentially connects a plurality of spark plugs 17 to the secondary winding 12 of ignition coil 10 through the lead 13 and leads 18 through 23.

The primary winding 11 of ignition coil 10 is connected to the negative terminal 26 of a source of electrical energy or storage battery 27 through lead 28, diode 29, and lead 31. The diode 29 is poled to permit current flow from the ignition coil 11 to the negative terminal 26 of the battery 27, but to prevent current flow in the reverse direction. The other terminal of the primary winding 11 of ignition coil 10 is connected to an output electrode-32, in the form of a collector, of a solid state switching device, preferably in the form of a transistor 33 through lead 34, lead 35, winding 36, and lead 37. The other output electrode 38 of this solid state switching device or transistor 33, shown in the form of an emitter, is connected to the positive terminal 41 of the source of electrical energy or battery 27 through lead 42, lead 43, and lead 44. The lead 43 and hence the positive terminal 41 of the source of electrical energy 27 is connected to ground through a lead 45.

A saturable switching core or transformer 46 having a hysteresis loop schematically represented in FIGURE 2, is employed to control the conduction of the solid state switching device or transistor 33. This saturable switching core has a first winding 47 having its dot marked terminal connected to the positive terminal 41 of battery 27 through lead 48, movable arm 49, movable contact 50 of a set of ignition contact breaker points 51, the fixed contact 52 of this set of ignition contact breaker points, lead 53, lead 43, and lead 44. The other end or terminal of the winding 47 is connected through lead 54, resistor 55, lead 56, resistor 57, lead 59, and lead 31 to the negative terminal 26 of the source of electrical energy 27. A Zener diode 61 has its anode coupled between the junction of resistors 55 and 57 and its cathode connected to the lead 43 thereby connecting the Zener diode 61 across the winding 47 and in series with the resistor 57 across the source of electrical energy 27 The winding 36 previously referred to as connecting the one terminal of the primary winding 11 and the output electrode or collector 32 of the transistor 33, is wound upon the core or transformer 46 such that its dot marked terminal is connected to the primary winding 11 and the other terminal is connected to the output electrode or collector 32.

A third winding 65 in the form of a feedback winding has its dot marked terminal connected through lead 66 to a control electrode or base 67 of the solid state switching device or transistor 33, while the other end of the winding 65 is connected through lead 68 with the output or emitter electrode 38 of the solid state switching device or transistor 33.

A fourth winding 71 is wound upon the saturable switching core or transformer 41, and it has its dot marked terminal connected through lead 72, resistor 73, and lead 74 to the lead 31 and hence to the negative terminal 26 of the source of electrical energy 27. The other terminal of the winding 71 is connected through lead 72, to the lead 43 and hence to the positive terminal 41 of the source of electrical energy 27.

A capacitor 75 has one terminal connected through lead 76 to ground and hence the positive terminal 41 of the source of electrical energy 27 since this positive terminal is grounded through leads 44 and 45. The other terminal is connected through lead 77 to a junction 78 positioned between the diode 29 and the primary winding 11 of the ignition coil 10. The terminal of capacitor 75 that is coupled to the junction 78 is also connected to the junction 81 through a lead 82 and a diode 85.

An inductor 91 has one terminal connected to the junction 81 through a lead 92. The other terminal of the conductor 91 is coupled through diode 93 and lead 94 to the negative terminal 26 of the source of electrical energy 27. The diode is poled to permit current to flow from the inductor 91 toward the negative terminal 26 of the source of electrical energy 27, but to prevent current in the opposite direction.

The ignition contact breaker points 51 are normally biased to a closed position, and are separated or opened periodically by a cam 95 that operates a follower 96 coupled to the arm 49. This cam is operated in synchronism with the rotatable arm 14 of the distributor 16 as shown by the dotted line 97, and it is arranged so that the ignition contact breaker points 51 open just shortly before the rotating arm 14 makes contact with the leads 18 through 23 respectively of the distributor 16.

Operation Referring now to the hysteresis loop shown in FIG- URE 2, conventional current into a dot marked terminal of the windings on the saturable switching core or transformer 46 produces a negative magnetomotive force and a resultant negative flux in the core 46 that tends to bias it toward a negative state of saturation at the point A. On the other hand, conventional current flow into an unmarked terminal produces a positive magnetomotive force that biases the saturable switching core or transformer 46 toward a positive state of saturation at point B.

Similarly, a fiux change from a negative flux state toward a positive flux will produce a negative voltage at a dot marked terminal of a winding with respect to its unmarked terminal, and a flux change from a positive flux state toward a negative flux state will produce a positive voltage at a dot marked terminal of a Windingwith respect to its unmarked terminal.

Since the winding 71 is permanently connected to the source of electrical energy 27 and conventional current flows into the unmarked terminal of the winding 71, a magnetomotive force is produced by this winding that is proportional to the terminal voltage of the source of electrical energy or battery 27 in a direction tending to bias the saturable switching core 46 toward a positive state of saturation, designated by the point B. On the other hand, when the ignition contact breaker points 51 are closed so that the points and 52 are in contact, current flows into the dot marked terminal of the winding 42 on the saturable switching core or transformer 46 thereby producing a negative magnetomotive force tending to bias the core or transformer 46 toward a negative state of saturation at the point A.

The Zener diode 61 is poled to prevent current flow through it until its breakdown voltage is reached. A Zener diode may be selected with a breakdown volt-age in the neighborhood of six volts for use with a storage battery ordinarily used with an automotive internal combustion ignition system having a nominal terminal voltage of twelve volts. As a result, a constant voltage is impressed across the winding 47 and resistor that produces a constant magnetomotive force in a negative direction independent of and irrespective of the terminal voltage of the battery 27. This negative magnetomotive force is opposed by the positive magnetomotive force produced by the winding 71. The current through the windings 47 and 71 and the number of turns of these windings is such that the operating point on the hysteresis loop as shown in FIGURE 2 is set at a point above the negative point of saturation, designated by the letter A. The purpose of this will be more fully explained subsequently. With the ignition contact breaker points 51 closed, therefore, the saturable switching core or transformer 46 will contain a flux that establishes an operating point dependent upon the terminal voltage of the source of electrical energy or battery 27, for example, at the point B.

Upon the opening of the contact breaker points 51, the negative magnetomotive force on the saturable switching core or transformer 46 resulting from the winding 47 is removed, and the core will be driven toward its positive state of saturation at the point B by the magnetomotive force produced by the winding 71. This change in flux cause a voltage to be induced in the feedback winding such that the base 67 of the solid state switching device ortransistor 33 is biased to a negative potential with respect to the output electrode or emitter 38. This turns the transistor or solid state switching device 33 to its conducting state, and current flows from the positive terminal 41 of the source of electrical energy or battery 27 through the solid state switching device or transistor 33 via lead 44, lead 43, output electrode or emitter 38, and output electrode or collector 32. This current then flows back to the negative terminal 26 of the source of electrical energy or battery 27 through lead 37, winding 36, lead 35, junction 81, primary winding 11 of the ignition coil 10, diode 29, and lead 31. Current also flows from the junction 81 to the negative terminal 26 of the source of electrical energy 27. through lead 92, inductor 91, diode 93, and lead 94.

It can be appreciated that current through the winding 36 is limited only by the internal resistances of the primary winding 11 and the inductor 91. It is sufiiciently large to drive the saturable switching core 46 to its positive state of saturation at the point B, since the current in a conventional sense is flowing into the unmarked terminal of the winding 36.

When this saturated condition is reached, a voltage is no longer induced in the feedback winding 65 coupling the control or base electrode 67 withthe emitter or output electrode 38 of the solid state switching device or transistor 33. As a result, the transistor or solid state switching device 33 is switched to its nonconducting state.

When the solid state switching device or transistor 33 switches to its nonconductive state, current therethrough is interrupted. It can be appreciated, however, that the current in the inductor 91 and the primary winding 11 of the ignition coil must continue to flow since current through these inductors cannot be interrupted instantaneously. The current from the inductor 91, therefore,

continues to flow through the diode 93, through lead 94, through the source of electrical energy or storage battery 27, through lead 44, and lead 45 to ground. From there, it flows through the capacitor 75 that is connected to ground through lead 76, thence through lead 82, diode 85, junction 81 and lead 92 to the opposite side of the inductor 91. This current flow is, of course, on a transient basis and it charges the capacitor 75 to a voltage level determined by the current in the inductor 91 at the time the transistor or solid state switching device 33 switches to a nonconducting state and by the parameters of the where I is the current in the inductor 91 just prior to the time that the transistor or solid state switching device 33 is switched to a nonconducting state. The voltage on the plate or terminal of the capacitor 75 coupled to the primary winding 11 of the ignition coil 10 via lead 77 and junction 78 is of a negative polarity and may be, by selection of the inductor and capacitor,- of a magnitude of approximately 100 volts;

Current through the primary winding 11 of the ignition coil 10 will continue to flow through the loop comprising the primary winding 11, junction 78, lead 77, lead 82, diode 85, terminal 81, and the lead 34. This current will finally be dissipated by the internal resistance of the primary winding 11. 1 v

When the capacitor becomes charged to'the abovementioned voltage after a short period of time, the saturable switching core or transformer 46 willthen be positioned at a point on the hysteresis loop shown in FIGURE 2 determined by the magnetomotive force flowing through the winding 91 prior to the closing of the ignition contact breaker points 51. When these ignition contact breaker points 51 close, the core "will be reset to its original operating point by'the magnetomotive force produced by current through the winding 47. I, 7

Upon the opening of the contact...breaker points 51, the saturable switching core 46 will again be switched toward its positive state of saturation at the point B thereby inducing in the feedback winding 65 a negative voltage at the dot marked terminal with respect to the unmarked terminal. This switches the solid state switching device or transistor 33 into its conducting state and the capacitor 75 discharges through the primary winding 11 of the ignition coil 10 by drawing current from the positive terminal 41 of the source of electrical energy 27, through lead 44, lead 43, lead 42, solid state switching device or transistor 33, lead 37, winding 36, lead 35, junction 81, lead 34, primary winding 11 of the ignition coil 10 to the terminal of the capacitor 75 coupled to the lead 77. This discharge induces high ignition voltages in the secondary winding 12 of the ignition coil 10 as disclosed by the high initial spike of voltage shown in FIG URE 3. This high initial spike of voltage occurs when the rotating arm 14 of the distributor 16 is in contact with one of the leads 18 through 23 to apply this high spike of voltage to one of the spark plugs 17. After this voltage has broken down the spark gap in the ignition devices or spark plug 17, current may continue to flow through the primary winding 11 of the ignition coil 10, through the solid state switching device or transistor 33 which is now in a conducting state and back to the negative terminal 26 of the source of electrical energy or battery '27, through the diode 29 thereby inducing in the secondbe charged when the solid state switching device or transistor 33 switches to its nonconducting state upon the saturation of the saturable switching core 46 as previously explained. The saturable switching core will then be reset to its original operating point uponthe closing of the ignition contact breaker points 51 and the cycle will repeat when the ignition contact breaker points 51 open.

If the lower voltage shown in FIGURE 3 that occurs after the discharge of the capacitor as previously explained, it is not necessary as the case may be for certain applications, then the diode 29 may be eliminated and the connection between the lead 31 and the junction 78 open circuited. The only voltage induced in the secondary winding 12, therefore, will occur as a result of the discharge of capacitor 75 through the primary winding 11.

The ignition system of the present invention provides a constant charge of electrical energy for the capacitor 75 irrespective and independently of engine speed and of the terminal voltage of the source of electrical energy 27. It can readily be appreciated from an inspection of FIG- URE 2 that the amount of time that the inductor 91 is energized from the source of electrical energy 27 depends upon the time that the solid state switching device or transistor 33 is energized. This on time for the solid state switching device or transistor 33 is in turn dependent on the time required for the saturable switching core or transformer 46 to switch from its given operating point to its positive state or saturation at the point B.

The winding 71 is positioned upon the core to produce a magnetomotive force that is in opposition to the magnetomotive force produced by the winding 47. As indicated in FIGURE 2, the winding 71 produces a magnetomotive force in the positive direction of the axis shown while the winding 42 produces a magnetomotive force in the opposite or negative direction. As was stated previously, the magnetomotive force applied by the winding 71 is dependent on and is proportional to the terminal voltage of the battery 27, since this winding is connected directly across the source of electrical energy or battery 27. These values may be so selected that the switching time for switching the saturable switching core or transformer 46 from different operating points to the saturated condiiton at B is determined by the terminal voltage of the source of electrical energy or battery 27 and is inversely proportional to this terminal voltage. Since the inductor 91 is coupled directly to the source of electrical energy 27 when the solid state switching device or transistor 33 is in its conducting state, it will receive energy at a rate that is directly proportional to this terminal voltage. Therefore, as the terminal voltage of the source of electrical energy or battery 27 changes, these two factors offset each other and provide for a substantially constant amount of electrical energy to be stirred in the inductor 91 for each ignition cycle. As stated previously, this electrical energy stored in the inductor 91 is stored in the capacitor 75 when the transistor or solid state switching device 33 switches to its nonconducting state.

This may be brought about by selecting a saturable core in which the hysteresis loop is a substantially straight line for a given distance oneither side of the origin. As stated previously, the voltage applied to the winding 47 is substantially a constant irrespective of the terminal voltage of the battery 27 due to the action of the Zener diode 61. As a result, the magnetomotive force applied to the core 46 from this winding is substantially constant. On the other hand, the magnetomotive force applied by the winding 71 to the core 46 varies in proportion to the terminal voltage. As a result, if the magnetomotive force applied by the winding 47 is selected to be approximately equal to the magnetomotive force applied by the winding 71 when the terminal voltage of the battery 27 is at its nominal voltage or twelve volts, these magnetomotive forces will tend to cancel each other and the operating point will be at the point H. On the other hand, should the terminal voltage of the battery drop to somewhat in the region of six volts, the magnetomotive force applied by the winding 47 will be double that applied by the winding 71 and the operating point of the core will be approximately at the point C. If the terminal voltage should rise to somewhat in the neighborhood of eighteen volts for some reason, the operating point will be at the point I. The distances from the point C to the point B, which is a measure of the on time of the solid state switching device or transistor 33, is three times that distance from the point I to the point B, and from the point H to the point B is twice the distance from the point I to the point B. Therefore, as the terminal voltage of the battery rises, the switching times for switching the core from its operating point determined by the terminal voltage of hte battery 27 will vary inversely as that terminal voltage thereby providing an energizing time for the inductor 91 that is inversely proportional to the terminal voltage of the battery 27.

It can be appreciated that the on time of the transistor or solid state switching device 33 is independent of engine speed since this on time is determined by the switching time switching the core 46 from its operating point to the saturated state when the contact breaker points 51 open. The parameters are so selected that the core 46 saturates in a few milliseconds, and at all times prior to the time that the ignition contact breaker points 51 close to reset the core back to its original Operating point by applying voltage across and current through the winding 47.

The 'present invention thereby provides a capacitive type discharge system for an automotive vehicle in which the energy stored in the capacitor and discharged into the system is substantially independent of engine speed and of the terminal voltage of the battery 27. This result may be accomplished without any alteration in the timing mechanism found in a conventional ignition system now in use with internal combustion engines for automotive vehicles.

It is to be uderstood that this invention is not to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An ignition system for an internal combustion engine comprising, a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, ignition actuating means operable in synchronism with the engine and actuated when said means couples said secondary winding of said ignition coil to each of said spark plugs, a capacitor having a first terminal and a second terminal, said first terminal coupled to said primary winding of said ignition coil, circuit means coupled to said source of electrical energy, said ignition actuating means, said first terminal of said capacitor and said primary winding of said ignition coil for storing a predetermined constant charge of electrical energy in said capacitor irrespective of the speed of the engine when said ignition actuating means is actuated and for discharging said charge of electrical energy in said capacitor through said primary winding of said ignition coil on the next successive actuation of said ignition actuating means, said circuit means including an inductor connected in series with the output electrodes of said solid state switching device and with one terminal of said source of electrical energy, a unilateral conducting device connected in series with said inductor and said one terminal of said source of electrical energy, said unilateral conducting device being poled to permit current flow from said inductor to said one terminal of said source of electrical energy and to prevent current flow from said one terminal of said source of electrical energy to said inductor, and circuit means connecting the second terminal of said capacitor with the other terminal of said source of electrical energy.

2. An ignition for an internal combustion engine that operates over a wide speed range comprising, an electrical storage battery, an ignition coil including. a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, ignition actuating means operable in synchronism with the engine and actuated when said means couples said secondary winding of said ignition coil to each of said spark plugs, a capacitor, a solid state switching device including a pair of output electrodes and a control electrode, said capacitor, said primary winding and said output electrodes of said solid state switching device connected in series, circuit means coupled to said electrical storage battery, said ignition actuating means and said capacitor for charging said capacitor to a pre determined constant electrical energy level irrespective of the speed of the engine when said ignition actuating means is actuated, and means coupled to said circuit means and said control electrode of said solid state switching device for switching said solid state switching device to a conducting state upon the actuation of said ignition actuating means whereby the electrical energy stored on said capacitor is discharged through said primary winding, said circuit means including an inductor connected in series with the output electrodes of said solid state switching device and with one terminal of said electrical storage battery.

3. The combination of claim 2 in which a unilateral conducting device is connected in series with one terminal of said electrical storage battery and said inductor and is poled to permit current flow from said inductor to said one terminal of said source of electrical energy and to prevent current flow from said source of electrical energy to said inductor.

4. An ignition system for an internal combustion engine comprising, a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, ignition actuating means operable in synchronism with the engine and actuated when said means couples said secondary winding of said ignition coil to each of said spark plugs, a capacitor, a solid state switching device including a pair of output electrodes and a control electrode, said capacitor, said primary winding and said output electrodes of said solid state switching device connected in series, circuit means coupled to said source of electrical energy, said ignition actuating means and said capacitor for charging said capacitor to a predetermined constant electrical energy level irrespective of the terminal voltage of said source of electrical energy when said ignition actuating means is actuated, and means coupled to said circuit means and said control electrode of said solid state switching device for switching said solid state switching device to a conducting state upon the actuation of said ignition actuating means whereby the electrical energy stored on said capacitor is discharged through said primary winding, said circuit means comprising an inductor connected in series with the output electrodes of said solid state switching device and with said source of electrical energy, and a unilateral conducting device connected in series with said inductor and said source of electrical energy and is poled to permit current flow from said inductor to said source of electrical energy and to prevent current flow 5 from said source of electrical energy to said conductor.

References Cited UNITED STATES PATENTS 3,169,212 2/1965 Walters 315223 10 Loudon et a1. 123148 Hufton 123148 Motto 123--148 Sturrn 315223 Boyer 123-148 JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

